Dyfed

One day Dyfed visited Glacian, the master artificer of the Thran Empire and a latent planeswalker himself, wanting to meet the genius in real life. Yawgmoth, then the most important healer of the empire, walked in on the meeting and managed to talk Dyfed into aiding him. Dyfed agreed to find a plane where Yawgmoth could build his own paradise. Sometime later, as Yawgmoth amassed more and more power, but also drove the empire to war with the people of nations he had harmed in the past, Dyfed opened a permanent portal from Dominaria to Phyrexia, the metal plane which Yawgmoth wanted to make his paradise.

However, at the same time Dyfed was starting to see that aiding Yawgmoth was a mistake. Rebbec and Glacian convinced her to rescue the elders of the empire, whom Yawgmoth had imprisoned. She took them, along with a number of goblin servants, to the plane of Mercadia, where they would become the ancestors of the Mercadians, and the Kyren.

Dyfed then planeswalked to Phyrexia, where she met with Yawgmoth, claiming to be there to put an end to his plans. Yawgmoth stabbed her in the skull with a powerstone blade that scrambled her brain, preventing her from defending herself and from switching off her immortality or planeswalking away. Thus Yawgmoth had his minions vivisect her, hoping to find an organ that allowed for planeswalking and have it transplanted into himself. However, before any such organ could be discovered, Rebbec found the tortured planeswalker and removed the powerstone from her skull, allowing her to die.